Pour point testing

Pour-Point Depressants. The pour point of alow viscosity paraffinic oil may be lowered by as much as 30—40°C by adding 1.0% or less of polymethacrylates, polymers formed by Eriedel-Crafts condensation of wax with alkylnaphthalene or phenols, or styrene esters (22). As wax crystallizes out of solution from the Hquid oil as it cools below its normal pour point, the additive molecules appear to adsorb on crystal faces so as to prevent growth of an interlocking wax network which would otherwise immobilize the oil. Pour-point depressants become less effective with nonparaffinic and higher viscosity petroleum oils where high viscosity plays a dominant role in immobilizing the oil in a pour-point test. 

When pour point testing is performed on crude oil, little to no shear is applied to the oil in the pour point tube. Under these conditions, the wax crystal lattice matrix which forms in the crude oil normally remains intact and the oil gels at the pour point. 

If shearing has destroyed the loosely formed wax lattice network of gelled crude oil so that the oil flows below its natural pour point, heating can restore the oil to its original pour point. By heating the crude oil to temperatures 20°F to 30°F (11.1 °C to 16.7°C) above the cloud point, waxes can be melted, solubilized and redistributed into the oil. When the pour point is then determined for this heated oil, the result obtained may be higher than the result obtained for the same oil which was not heated prior to pour point testing. All wax must be melted and solubilized into... 

When determining the pour point of certain heavy residual products such as 6 fuel oils, bunker fuels, vacuum gas oils, vacuum resids, atmospheric resids, and visbreaker bottoms, it is important to pay close attention to the temperature applied to the oil prior to pour point testing. In some cases, preheating an oil to temperatures greater than 212°F (100°C) prior to pour point testing can result in a pour point value which is lower than the value obtained for the same oil preheated to 110°F (43.3°C). 

The pour point test is used to determine the lowest temperature at which a fuel can be effectively pumped. However, the pour point value can be misleading, especially when it is used to determine the low-temperature handling characteristics of residual fuel oil and other heavy fuels. Low-temperature viscosity measurements are considered more reliable than pour point values for determining the flow properties and pumpability of these oils. 

This procedure can be utilized to determine whether heavy fuel wax crystal modifiers will lose their performance properties after long-term storage at fluctuating temperatures. Daily heating and overnight cooling may interfere with the ability of some wax crystal modifiers to maintain their performance properties in some residual oils and crude oils. This loss of performance is frequently termed pour point reversion. The British Admiralty Pour Point Test can be utilized to help predict these reversion tendencies. 

An oil sample treated with a wax crystal modifier is heated to 200°F (93°C) and poured immediately into pour point test jars fitted with a thermometer capable of reading temperatures from -35°F (-37°C) to 210°F (100°C). 

Allow the sample in the pour point test jars to cool to 120°F (49°C), and then place the tubes into a -30°F (-34°C) cold well. Allow the test jars to remain in the bath until the temperature of the oil is 0°F (-18°C). 

Once cooled, place the oil sample into the pour point test well maintained at 30°F (-1°C). Conduct the remainder of the test as described in ASTM D-97 by checking the pour point every 5°F (3°C). 

Compare the pour point obtained with the value determined from a standard ASTM D-97 pour point test. If the pour point temperature obtained is higher than the standard ASTM D-97 value, a reversion in pour point has occurred. 

Once heated, pour a sample of oil into a pour point test jar to a height of approximately 57 mm. Place a cork carrying the thermometer on the test jar and set the sample into a -40°F ( 40°C) test well. 

Fuel Oils, Analytical. The following determinations were made at US War Planes during WWII 1) Specific Gravity 2) Moisture 3) Insolubles 4) Flash Point and 5) Pour Point Tests... 

In any determination of the pour point, petroleum that contains wax produces an irregular flow behavior when the wax begins to separate. Such petroleum possesses viscosity relationships that are difficult to predict in pipeline operation. In addition, some waxy petroleum is sensitive to heat treatment that can also affect the viscosity characteristics. This complex behavior limits the value of viscosity and pour point tests on waxy petroleum. However, laboratory pumpabUity tests (ASTM D-3245, IP 230) are available that give an estimate of minimum handling temperature and minimum line or storage temperature. 

Although the pour point test is still included in many specifications, it is not designated for high-boiling fuel oil (ASTM D 396). In fact, although the failure to flow at the pour point normally is attributed to the separation of wax from the fuel oil (in the case of waxy crude oil precursors), it also can be due to the effect of the viscosity of the fuel oil (in the case of naphthenic crude oil precursors). In addition, the pour point of fuel oil may be influenced by the previous thermal history of the fuel oil. Thus the usefulness of the pour point test in relation to fuel oil, especially residual fuel oil, may be open to question. 

The pour point of residual fuel oil may be influenced by the previous thermal history of the residual fuel oil and the fact that any loosely knit wax structure built up on cooling the fuel can, generally, be readily broken up by the application of a little pressure, thus allowing fuels to be pumped at temperatures below their pour point temperatures. The usefulness of the pour point test in relation to residual fuel oils is, therefore, open to question, and the tendency to regard it as the limiting temperature at which a fuel will flow can be misleading unless it is correlated with low-temperature viscosity. 

The pour point test is still included in many specifications but not in some (ASTM D-396, BS 2869) for assessing the pumpability characteristics of residual fuel oil (ASTM D-3245). Pour point procedures involving various preheat treatments before the pour point determination and the use of viscosity at low temperatures have been proposed. The fluidity test (ASTM D-1659) is one such procedure as is the pumping temperature test (ASTM D-3829) another test, based on viscosity measurements (IP 230), is also available. 

In the pour point test (ASTM D-97, IP 15), the oil is heated to a specified temperature that is dependent on the anticipated pour point range, cooled at a specified rate, and examined at 3°C (5°F) intervals for flow. The lowest temperature at which no movement of the oil is detected is recorded. The 3°C (5°F) temperature value immediately preceding the recorded temperature is defined as the pour point. 

The pour point of a lubricant is determined by the ASTM D97 pour point test. In summary, the method records the temperature of the oil at 3°C above the point at which the oil will not move when tipped out of the horizontal. 

XI.1.1 The low-temperature flow properties of a waxy fuel oil depend on handling and ston conditions. Thus, they may not be truly indicated by pour point. The pour point test does not indicate what haqppens when an oil has a considerable head of pressure behind it, such as when gravitating from a storage tank or being pumped along a pipeline. Failure to flow at the pour point is normally attributed to the separation of wax from the fuel however, it can also be due to the effect of viscosity in the case of very viscous fuel oils. In addition pour points of residual fuels are influenced by the previous thermal history of the specimens. A loosely knit wax structure built up on cooling of Ae oil can be normally broken by the application of relatively little pressure. 

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